The present invention relates to techniques for improving the controllability of output power of a high frequency power amplification circuit by a power control signal and for ramping up without fail the output power of the high frequency power amplification circuit upon starting, and more particularly, to techniques suitable for application in a semiconductor integrated circuit for communication which contains a phase detection circuit and an amplitude detection circuit, and a radio-communications apparatus such as a portable telephone which incorporates the semiconductor integrated circuit for communication.
One of conventional schemes for radio-communications apparatus (mobile communication apparatus) such as a portable telephone is GSM (Global System for Mobile Communication) which is employed in Europe. This GSM scheme uses a phase modulation mode called GMSK (Gaussian Minimum Shift Keying) which shifts the phase of a carrier in accordance with transmission data.
Generally, a high frequency power amplification circuit is incorporated in a transmission output unit in a radio-communications apparatus. A conventional GSM-based radio-communications apparatus employs a configuration for controlling a bias voltage of a high frequency power amplification circuit to provide output power required for a call by means of a control voltage outputted from a circuit, called an APC (Automatic Power Control) circuit, which generates a control signal for a transmission output based on a signal from a detector for detecting a transmission output and a level required for transmission from a baseband LSI.
In recent portable telephones, an EDGE (Enhanced Data Rates for GMS Evolution) scheme has been proposed. The EDGE scheme has dual-mode communication functions, and relies on GMSK modulation to perform audio signal communications and on 3π/8 rotating 8-PSK (Phase Shift Keying) modulation to perform data. communication. The 8-PSK modulation is such modulation that adds an extra amplitude shift to a phase shift of a carrier in the GMSK modulation. Since the 8-PSK modulation can send 3-bit information per symbol, in contrast with the GMSK modulation which sends 1-bit information per symbol, the EDGE scheme can achieve communications at a higher transmission rate as compared with the GSM scheme.
As one implementation of a modulation mode for imparting information on a phase component and an amplitude component, respectively, of a transmission signal, there is a conventionally known configuration called “polar loop” which involves separating a signal intended for transmission into a phase component and an amplitude component, subsequently applying feedback to the separated components through a phase control loop and an amplitude control loop, and combining the resulting components by an amplifier for outputting the combined components (for example, “High Linearity RF Amplifier Design” by Kenington, Peter B., p 162, published by ARTECH HOUSE, INC. in 1979).
A GSM-based communication system is only required to output a phase modulated signal in accordance with a required output level, so that a high frequency power amplification circuit at a final stage can be operated in a saturation region, whereas a radio-communications system capable of transmission/reception in the 8-PSK modulation mode must perform an amplitude control, so that a high frequency power amplification circuit at a final stage must be linearly operated in a non-saturation region. However, with a method of driving a high frequency power amplification circuit used in a conventional GSM-based communication system, it is difficult to ensure the linearity which is required by the high frequency power amplification circuit in a small output level region. On the other hand, the polar loop configuration can advantageously satisfy the requirement for the linearity of the high frequency power amplification circuit, and improve the power efficiency in the low output level region.
The GSM-based communication system is only required to output a phase modulated signal in accordance with a required output level, so that a high frequency power amplification circuit at a final stage can be operated in a saturation region, whereas a radio-communications system capable of EDGE-based transmission/reception must perform an amplitude control, so that a high frequency power amplification circuit at a final stage must be linearly operated in a non-saturation region. However, with a method of driving a high frequency power amplification circuit used in a conventional GSM-based communication system, it is difficult to ensure the linearity which is required by the high frequency power amplification circuit in a small output level region. On the other hand, the polar loop configuration can advantageously satisfy the requirement for the linearity of the high frequency power amplification circuit, and improve the power efficiency in the low output level region.